Heretofore, sulfur containing compounds have been prepared by reacting hydroxyl-terminated dimethylpolysiloxane fluids with a methoxy containing silacyclopentane thiol in the presence of an acid clay to affect the condensation reaction of the sulfur containing silane and the dimethylpolysiloxane. In the condensation reaction, the acid clay not only catalyzes the condensation between the methoxy groups of the sulfur containing compound and the hydroxyl groups of the dimethylpolysiloxane but also catalyzes the condensation between hydroxyl groups to form a mixture of compounds. Furthermore, the process requires that a preformed hydroxyl-terminated dimethylpolysiloxane fluid be prepared prior to the condensation reaction.
Viventi discloses in U.S. Pat. No. 3,346,405, a process for preparing sulfur containing siloxanes by reacting sodium sulfohydride with w-chloroalkyl containing organopolysiloxanes in the presence of dimethylformamide. Also, U.S. Pat. No. 2,960,492 to Morton et al disclose a process for preparing sulfur containing organopolysiloxanes by reacting a vinyl containing siloxane with a mercaptan to form an adduct therewith by combining the sulfohydride group with the unsaturated vinyl group of the siloxane. U.S. Pat. No. 3,388,144 to Musolf et al discloses reacting a siloxane containing one or two mercaptoalkyl groups per silicon atom with a polyhydroxylated carbon compound containing an unsaturated olefin group in the presence of a peroxide catalyst.
The above described processes for preparing thiofunctional siloxane polymers have several disadvantages. For example, long reaction times are required. Also, siloxanes having chloroalkyl groups or vinyl unsaturation are required as one of the reactants. Moreover, it is very difficult to obtain complete conversion of the chloroalkyl groups or vinyl groups to thiofunctional groups, thus polymers having both functional groups are obtained from the above processes.
U.S. Pat. No. 4,046,795 to Martin discloses a process for preparing thiofunctional polysiloxane polymers by reacting a disiloxane and/or a hydroxy or hydrocarbonoxy containing silane or siloxane with a cyclic trisiloxane in the presence of an acid catalyst, in which at least one of the silanes or siloxanes contain a thiol group. However, when a cyclic siloxane containing more than three silicon atoms, e.g., octamethylcyclotetrasiloxane, is substituted for hexamethylcyclotrisiloxane, there is no detectable reaction observed in the presence of an acid catalyst. Surprisingly, it has been found that the thiofunctional polysiloxane polymers prepared in accordance with U.S. Pat. No. 4,046,795 will further react with siloxanes having more than three silicon atoms in the molecule in the presence of an acid catalyst to form higher molecular weight thiofunctional polysiloxane polymers. This process is of commercial significance since it now provides a means for utilizing organopolysiloxanes such as cyclic siloxanes having more than three silicon atoms per molecule in the preparation of thiofunctional polysiloxane polymers.
Therefore, it is an object of this invention to provide a method for preparing thiofunctional polysiloxane polymers which do not require vinyl unsaturation or chloroalkyl substituents. A further object of this invention is to provide a method for preparing a broad spectrum of thiofunctional polysiloxanes from siloxanes having more than three silicon atoms per molecule in the presence of an acid catalyst.